The velopharynx is a critical component of the speech production mechanism. When adults speak, the velopharynx is closed most of the time, especially during oral (nonnasal) sound production. In contrast, when very young infants produced sound, the velopharynx is usually open. Surprisingly, the age at which the velopharynx closes consistently for oral sound production is still not known. The study proposed in this application is designed to follow healthy children longitudinally until consistent velopharyngeal closure is observed. It will address the following specific aims: (a) to determine the age at which velopharyngeal closure occurs consistently for oral sound production; and (b) to determine if phonetic, linguistic, and/or motor variables help to explain differences in velopharyngeal function during oral sound production within and among children. The study will include 60 children (equal numbers of boys and girls), beginning at age 4 months, with observations being made monthly until consistent closure is observed for 3 consecutive months. The status of the velopharynx (open vs closed) will be determined using a noninvasive aeromechanical approach (developed in our laboratory) that involves the monitoring of nasal air pressure in relation to the acoustic signal. Vocalizations/speech will be elicited using toys, facial expressions, picture books, imitation, and verbal probes, depending on the age of the child at the time. Measures reflecting the child's phonetic repertoire, expressive and receptive language skills, and motor development will also be obtained during each session, and will be used to help explain any variability not accounted for by age. The results of this study will answer a question that is fundamental to the understanding of normal speech development (At what age does the velopharynx close consistently for oral sound production?). By doing so, it will also lay the groundwork for future research on infants who are at risk for impairment of velopharyngeal function, such as those with known or suspected neuromotor disorders, and for eventual application to clinical evaluation and management of such infants.